1. Field of the Invention
The present disclosure relates to a battery state estimation method and system using a dual extended Kalman filter and a recording medium for performing the method, and more particularly, to a battery state estimation method and system using a dual extended Kalman filter and a recording medium for performing the method, in which a battery state may be calculated in consideration of hysteresis and diffusion phenomena.
2. Discussion of Related Art
Along with the rapid increase in demand for portable electronic products such as a notebook, a video camera, and a cell phone and the full-scale development of capacitors for storing energy, robots, and satellites, research is being conducted on high-performance secondary batteries that can be repeatedly charged and discharged.
Commercially available secondary batteries include a nickel-cadmium battery, a nickel-metal hydride battery, a nickel-zinc battery, a lithium secondary battery. From thereamong, the lithium secondary battery is getting the spotlight because the lithium secondary battery has almost no memory effect, and thus the lithium secondary battery provides several advantages e.g., charging/discharging with less memory effects, a high self-discharge rate, and a high energy density.
In particular, recently, as carbon energy is increasingly exhausted and public interest in the natural environment increases, the demand for hybrid vehicles and electric vehicles has been increased gradually and globally including in the United States, Europe, Japan, and South Korea. Such a hybrid or electric vehicle has been received a good response from market since the hybrid or electric vehicle is provided with a driving force from a battery pack by charging/discharging energy thereof. The hybrid or the electric vehicle is more energy efficient and reduces pollution emissions. Accordingly, a vehicle battery has been received attentions nowadays since the vehicle battery is regarded as an essential component of the hybrid or the electric vehicle.
Since a battery is used for various types of mobile devices such as a notebook or a vehicle and has a limited lifespan with proper functionality, it is important to measure accurate information on a state of charge (SOC) of the battery. The SOC is one of parameters as to how long the battery can last, and thus is very important information when a user uses a device receiving a power from the battery. Conventional battery-equipped devices such as a notebook, a cell phone, and a vehicle may estimate an SOC of the battery and then may provide the user with the information including an available time period or the charged amount of the battery on a basis of the estimated SOC.
The SOC of the battery is generally displayed in a form of a percentage of the remaining amount with respect to a full charge capacity (FCC) of the battery. A variety of methods of estimating the SOC of the battery may be used, and one of conventional methods is a method of estimating the SOC using the Coulomb counting method. The Coulomb counting method is a scheme of finding the SOC by accumulating input/output currents of the battery and adding/subtracting the accumulated currents to/from an initial capacity. However, the Coulomb counting method may provide a limited accuracy when there is an error in an initial value of the SOC or when an error of a measured current is accumulated over time. A method of estimating the SOC and a state of health (SOH) using a Kalman filter may be used to overcome the limitation. In order to increase an accuracy of the estimation, a battery module and its parameters should be accurate. The information of the changes in the parameters should be accurately considered. However, it is not easy to obtain such accurate information because it requires more time and equipment. Furthermore, if the type or capacity of the battery is not the same, a new test should be conducted again and it adds more trouble. In addition, for the parameters of the battery, the estimated accuracy of the SOC/SOH of the Kalman filter would be decreased as the battery is aging because their parameter values would be changed over time.